10 observed values for
parent and F1 and 50 ones for F2 were sampled
randomly per plot, respectively, and plot means were calculated.
Analysis of variance on a plot mean basis was conducted for parents,
F1's and F2's, respectively. Since differences
between their error variances were not significant, analysis of
variance and combining ability was carried out for the F1
and parents, and F2 and parents, respectively (Singh and
Chaudhary 1979; Guo 1993).
Genetic parameters such as heritability and average degree of
dominance were estimated on the random model or Model II in
Table 3
(Guo 1993).
Additionally,
simple correlations were computed for parent versus F1,
parent versus F2 and F1 versus F2,
on the basis of genotype means and combining ability effects.
Results
Performance of genotypes in resistance to scab
The averages of scab-diseased spikelets for the parents,
F1 crosses and F2 populations are given in
Table
1. Overall
generation means for the diseased spikelets were 3.92,
3.40 and 3.82 for parent, F1 and F2,
respectively, and the coefficients of variation were 24.04% for
F1 and 25.28% for F2. Of all parents, W14 was
the most resistant, superior to Sumai 3. For most combinations,
averages of numbers of diseased spikelets of F1 and
F2 were less than mid-parent values, indicating that
dominance for resistance existed. The average number of diseased
spikelets of F2 was larger than that of F1
though differences between both generation means and error variances
were not significant. On average of all combinations, number of
diseased spikelets of F1's was significantly less than
that of midparent values. However, there was no significant
difference between F2's and midparent values.
Analysis of variance showed
that there were highly significant differences
in scab resistance among parents, among F1's and among
F2's (Table
2).
The 'female versus male'
effect and 'parent versus F1' effect were also highly
significant but the 'parent versus F2' effect was
insignificant.
Combining ability analysis and effects of combining ability
As shown in Table
3, general
combining ability
(GCA) effects were
highly significant for both F1 and F2. It
indicates that both maternal and paternal parents have great
influences on the performance of their cross offsprings in resistance
to Fusarium graminearum. Relatively speaking, the effects of
the paternals were larger than those of the maternals. Specific
combining ability (SCA) effects were also highly significant in
F1 and F2. It is shown that the performance of
specific combination in resistance depends upon the resistance level
of two parents as well as the interaction of parents.
GCA effects of parents are
given in Table
1. Among the
resistant or paternal parents, W14 was of the highest resistance, and
greatest and significant GCA effects in both F1 and
F2. Clearly, it should be a good parent for breeding for
resistance to scab in wheat. The well-known resistant cultivar Sumai
3 possessed higher resistance (only second to W14), but did not have
good GCA effect in, F2 although its relative value of GCA
for F1 was 6.07% in decreasing diseased spikelets of
offsprings. Relative values of GCA of TFSL037 were 3. 06% and 4.36%
in F1 and F2, respectively. Compared with W14
and TFSL037, the GCA effects of Changjiang 8809 and Nantai 7 were
disadvantageous to increasing resistance in F1 and
F2. For the maternal parents or testers, Yangmai 5 and
Changjiang 8853 had higher resistance and general combining ability.
Aiganzao and Mianyang 11 had negative effects on performance of the
offsprings in the resistance.
Estimation of genetic parameters
Based on random model, variance between combinations, GCA variance of
maternal and paternal parents and SCA variance of their interaction
for F1 and F2, except GCA variance of maternals
and paternals in F1, were significant or highly
significant (Table
2 and
Table
3). Then genetic
parameters were estimated. Of the genetic variance, SCA variance
accounted for 55.22% and 50.91% respectively, in F1 and
F2, and GCA variance accounted for 44.78% and 49.09%.
Average degree of dominance was 1. 111 and 1.018 for F1
and F2, respectively, indicating that there was dominance
or superdominance in F1 and F2. Estimates of
broad-sense and narrow-sense heritability were 77.86% and 34.86% in
F1, and 90.34% and 44.35% in F2, respectively.
It is indicated that, in the inheritance of the resistance to scab in
wheat, the additive effects of resistance genes in F2
played a more important role than those in F1.
Correlation
Analysis of simple correlation on parent mean versus combination mean
showed that correlations between four maternals and F1
crosses and F2 populations, between five paternals and
F1 and F2, between mid-parent values and
F1's and F2's, and between parent mean and GCA
effects for F1 and F2 were not significant.
Simple correlation coefficients between maternal means and GCA
effects were 0.558 and 0.639 for F1 and F2, and
0.564 and 0.315 between paternal means and GCA effects for
F1 and F2, respectively. There was a
significant correlation between F1 and F2 for
combination means (r=0.616**) and for SCA effects (r=0.643**). For
GCA effects, however, correlation between F1 and
F2 was not significant (r=0.631).